1. Field of the Invention
The present invention relates to a regeneration control system and method of a hybrid vehicle which is driven by an engine and an electric motor, and in particular, relates to a system and method for preventing engine stall due to a sudden decrease of the engine speed during deceleration regeneration.
2. Description of the Related Art
Conventionally, a hybrid vehicle having not only an engine but also an electric motor as the drive source is known.
As a hybrid vehicle, a parallel hybrid vehicle is known that uses an electric motor as an auxiliary drive source for assisting the engine output. In the parallel hybrid vehicle, typically, operating the engine is assisted using the electric motor during the accelerating operation, while during the decelerating operation, the battery and the like are charged via a regenerating operation, that is, xe2x80x9cdeceleration regenerationxe2x80x9d is performed. According to various control operations including the above, the remaining capacity (called as xe2x80x9cstate of chargexe2x80x9d, hereinafter) of the battery is maintained while also satisfying the driver""s demands. An example thereof is disclosed in Japanese Unexamined Patent Application, First Publication, No. Hei 7-123509.
In such a conventional parallel hybrid vehicle, regenerated power obtained during deceleration can be stored so that the energy, which has been wastefully discharged, can be effectively used. It is profitable in power management. However, regeneration imposes a load on the engine. Therefore, when the engine (rotation) speed suddenly decreases during deceleration regeneration, if an excessive load generated by regeneration is imposed on the engine, then the engine may stall. If regeneration operation is significantly limited in order to solve such a situation, the amount of energy to be stored by executing regeneration is reduced and another means for increasing power generation is necessary. It is not profitable for reducing fuel consumption.
In consideration of the above circumstances, an objective of the present invention is to provide a regeneration control system and method applied to a hybrid vehicle, by which sufficient energy can be stored during deceleration regeneration, and engine stall can be prevented when the amount of load imposed on the engine increases during deceleration regeneration.
Therefore, the present invention provides a regeneration control system of a hybrid vehicle, wherein:
said hybrid vehicle comprises:
an engine for outputting force for driving the vehicle;
an electric motor for assisting the output from the engine; and
a battery device (refer to battery 3 in the embodiment of the present invention, later explained) for supplying electric power to the motor, and
said regeneration control system comprising:
a regeneration control section (refer to a motor ECU 1 in the embodiment) for determining a quantity of regeneration (refer to a final charge command value REGENF in the embodiment) performed using the motor during deceleration of the vehicle, and for making the motor execute regeneration based on the determined quantity;
an engine speed variation detecting section (refer to an FIECU 11 in the embodiment) for detecting a variation (refer to decrement DNE of the engine speed in the embodiment) of the engine speed; and
a regeneration stopping section for stopping regeneration executed by the motor during deceleration of the vehicle (for example, via a process of step S101 in the embodiment) if the variation of the engine speed detected by the engine speed variation detecting section is larger than a predetermined value (refer to a predetermined value #DNRGNCUT in the embodiment).
The present invention also provides a regeneration control method of a similar hybrid vehicle (comprising the above-explained engine, electric motor, and battery device), comprising the steps of:
determining a quantity of regeneration performed using the motor during deceleration of the vehicle, and for making the motor execute regeneration based on the determined quantity;
detecting a variation of the engine speed; and
stopping regeneration executed by the motor during deceleration of the vehicle if the detected variation of the engine speed is larger than a predetermined value.
Accordingly, if it is determined that the variation of the engine speed, which decreases during deceleration regeneration, is larger than the predetermined value, that is, if it is determined that the load imposed on the engine in regeneration is large with respect to the possible range of the engine speed (the engine may stall even if the engine speed is sufficiently high), the regeneration can be stopped, thereby removing the load imposed on the engine in regeneration. Therefore, engine stall can be prevented.
The regeneration control system may further comprise an engine speed detecting section (refer to an engine speed sensor S2 in the embodiment) for detecting the engine speed. In this case, the regeneration stopping section may stop regeneration executed by the motor during deceleration of the vehicle if the variation of the engine speed detected by the engine speed variation detecting section is larger than a predetermined value, or if the engine speed detected by the engine speed detecting section is equal to or below a predetermined value (refer to a predetermined value #NERGNCUT in the embodiment).
Similarly, the regeneration control method may further comprise the step of detecting the engine speed. In this case, it is possible to stop regeneration executed by the motor during deceleration of the vehicle if the detected variation of the engine speed is larger than a predetermined value, or if the detected engine speed is equal to or below a predetermined value.
Accordingly, even when the variation of the engine speed, which decreases during deceleration regeneration, is equal to or below the predetermined value, if the engine speed is equal to or below the predetermined value, that is, if the engine cannot independently rotate, then regeneration can be stopped and the load imposed on the engine in regeneration can be omitted. Therefore, engine stall can be prevented.
In the regeneration control system comprising such an engine speed detecting section, the regeneration stopping section may stop regeneration executed by the motor during deceleration of the vehicle if the variation of the engine speed detected by the engine speed variation detecting section is larger than a predetermined value, and if the engine speed detected by the engine speed detecting section is equal to or below a predetermined value.
Similarly, in the regeneration control method, it is possible to stop regeneration executed by the motor during deceleration of the vehicle if the detected variation of the engine speed is larger than a predetermined value, and if the detected engine speed is equal to or below a predetermined value.
Accordingly, if the variation of the engine speed, which decreases during deceleration regeneration, is larger than the predetermined value, and if the engine speed is equal to or below the predetermined value, then it is possible to further reliably determine the possibility of an engine stall; thus, the load imposed on the engine in regeneration can be omitted by stopping the regeneration. Therefore, engine stall can be prevented.